I am striving to identify what I am 99% confident to be a forgery. As part of a France collection for sale at an auction, the stamp at left below is stated to be the Napoleon 1 Fr official reprint, 1862. (Yvert 18d / Scott 21c).
(The stamp on the right is a certified authentic stamp 'stolen' from
ebay for reference). The differences are plentiful and obvious.

I have informed the seller I believe this to be a fake, however with no well argumented response. So I want to investigate myself, first of all I want to make a conclusion it is a forgery - and even better if it is possible to find out which forger made this spesific forgery.
I am confident I have seen a website with several different forgeries of the Napoleon issues before, but I am not able to find it again. Can anyone help me?